The origin of pancreatic islet cells, both during embryonic development and in a mature mammal, has remained uncertain despite intensive study. Certain ductal epithelial cells are capable of either differentiation or transdifferentiation to form beta cells and other cell types found in mature islets (Bouwens, 1998). Ductal cells from isolated islets can proliferate in culture and, if transplanted into an animal, can differentiate into functional beta cells (Cornelius et al., 1997).
It has been demonstrated that exendin-4, a long acting GLP-1 agonist, stimulates both the differentiation of β-cells from ductal progenitor cells (neogenesis) and proliferation of β-cells when administered to rats. In a partial pancreatectomy rat model of type 2 diabetes, the daily administration of exendin-4 for 10 days post pancreatectomy attenuated the development of diabetes. It has also been demonstrated that exendin-4 stimulates the regeneration of the pancreas and expansion of β-cell mass by neogenesis and proliferation of β-cells (Xu et al., 1999, Diabetes, 48:2270-2276).
Ramiya et al. have demonstrated that islets generated in vitro from pluripotent stem cells isolated from the pancreatic ducts of adult prediabetic non-obese diabetic (NOD) mice differentiate to form glucose responsive islets that can reverse insulin-dependent diabetes after being implanted, with or without encapsulation, into diabetic NOD mice (Ramiya et al., 2000, Nature Med., 6:278-282).
The insulinotropic hormone glucagon-like peptide (GLP)-1 which is produced by the intestine, enhances the pancreatic expression of the homeodomain transcription factor IDX-1 that is critical for pancreas development and the transcriptional regulation of the insulin gene. Concomitantly, GLP-1 administered to diabetic mice stimulates insulin secretion and effectively lowers their blood sugar levels. GLP-1 also enhances β-cell neogenesis and islet size (Stoffers et al., 2000, Diabetes, 49:741-748).
Ferber et al. have demonstrated that adenovirus-mediated in vivo transfer of the PDX-1 (also known as IDX-1) transgene to mouse liver results in the transconversion of a hepatocyte subpopulation towards a β-cell phenotype. It has been demonstrated that after intravenous infusion of mice with the PDX-1 adenoviral vector, up to 60% of hepatocytes synthesized PDX-1. The concentration of immunoreactive insulin was increased in the liver and serum of treated mice. Mice treated with PDX-1 survive streptozotocin-induced diabetes, and can even normalize glycemia (Ferber et al., 2000, Nature Med., 6:568-572).
While ductal cell cultures obtained from isolated islets apparently contain cells that can give rise to insulin-secreting cells, it has remained unclear whether those cells represent true stem cells or merely ductal epithelial cells undergoing transdifferentiation. Even if such preparations contain genuine stem cells, it is unknown what fraction represent stem cells and what contaminating cell types may be present. There is a need in the art for the isolation of specific cell types from pancreatic tissue, the cell types being characterized as stem cells using molecular markers and demonstrated to be pluripotent and to proliferate long-term.
Pluripotent stem cells that are capable of differentiating into neuronal and glial tissues have been identified in brain. Neural stem cells specifically express nestin, an intermediate filament protein (Lendahl et al., 1990; Dahlstrand et al., 1992). Nestin is expressed in the neural tube of the developing rat embryo at day E11, reaches maximum levels of expression in the cerebral cortex at day E16, and decreases in the adult cortex, becoming restricted to a population of ependymal cells (Lendahl et al., 1990). Developing neural and pancreatic islet cells exhibit phenotypic similarities characterized by common cellular markers.
The invention relates to a population of pancreatic islet stem/progenitor cells (IPCs) that are similar to neural and hepatic stem cells and differentiate into islet α-cells (glucagon) and β-cells (insulin). The invention also relates to nestin-positive liver cells. IPCs according to the invention are immunologically silent/immunoprivileged and are recognized by a transplant recipient as self. The IPCs according to the invention can be used for engraftment across allogeneic and xenogeneic barriers.
There is a need in the art for a method of engrafting stem cells across allogeneic and xenogeneic barriers.
There is also a need in the art for a method of treating type I diabetes mellitus wherein islets, nestin-positive pancreatic stem cells or nestin-positive liver stem cells are transferred into a recipient across allogeneic or xenogeneic barriers and graft rejection does not occur.